U.S. patent number 6,700,122 [Application Number 10/035,150] was granted by the patent office on 2004-03-02 for wafer inspection system and wafer inspection process using charged particle beam.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Miyako Matsui, Mari Nozoe, Atsuko Takafuji.
United States Patent |
6,700,122 |
Matsui , et al. |
March 2, 2004 |
Wafer inspection system and wafer inspection process using charged
particle beam
Abstract
The present invention provides a wafer inspection technique
capable of detecting a defect in a wafer on which a pattern having
a large step such as a contact hole being subjected to a
semiconductor manufacturing process is formed and obtaining
information such as the position and kind of a defect such as a
hole with open contact failure caused in dry etching process at
high speed. A wafer on which a pattern having a large step being
subjected to a semiconductor manufacturing process is formed is
scanned and irradiated with an electron beam having irradiation
energy which is in a range from 100 eV to 1,000 eV, and a defect is
detected at high speed from an image of secondary electrons
generated. Before the secondary electron image is captured, the
wafer is irradiated with an electron beam at high speed while being
moved to thereby charge the surface of the wafer with a desired
charging voltage. The kind of the defect is determined from the
captured secondary electron image, and a distribution of defects in
the plane of the wafer is displayed.
Inventors: |
Matsui; Miyako (Kokubunji,
JP), Nozoe; Mari (Hino, JP), Takafuji;
Atsuko (Tokyo, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
18939930 |
Appl.
No.: |
10/035,150 |
Filed: |
January 4, 2002 |
Foreign Application Priority Data
|
|
|
|
|
Mar 23, 2001 [JP] |
|
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2001-084232 |
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Current U.S.
Class: |
250/310;
250/492.2; 324/71.3; 324/754.22; 324/762.05 |
Current CPC
Class: |
H01J
37/28 (20130101); H01J 2237/281 (20130101); H01J
2237/2817 (20130101) |
Current International
Class: |
H01J
37/28 (20060101); G01R 031/26 () |
Field of
Search: |
;324/71.3
;250/310,492.2 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lee; John R.
Assistant Examiner: Leybourne; James J.
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP
Claims
What is claimed is:
1. A wafer inspection system using a charged particle beam,
comprising: a charged particle source; an objective lens for
irradiating a wafer on which a pattern including a hole pattern is
formed with a primary charged particle beam from said charged
particle source; a sample stage for holding said wafer; a charged
particle generator for positively charging the surface of said
wafer placed on said sample stage and the side wall of said hole
pattern formed on said wafer; a deflector for irradiating a
predetermined area in said wafer positively charged with a primary
charged particle beam; and a detector for detecting a secondary
charged particle from said wafer positively charged, wherein an
inspection is conducted on said hole pattern on the basis of a
signal from said detector.
2. The wafer inspection system using a charged particle beam
according to claim 1, wherein an electron source is provided as
said charged particle generator.
3. A wafer inspection system using a charged particle beam,
comprising: a charged particle source; an objective lens for
irradiating a wafer on which a pattern including a hole pattern is
formed with a primary charged particle beam from said charged
particle source; a sample stage for holding said wafer; a charged
particle generator for positively charging the surface of said
wafer placed on said sample stage and the side wall of said hole
pattern formed on said wafer; a deflector for scanning and
irradiating a predetermined area in said wafer charged by said
charged particle generator with a primary charged particle beam; a
detector for detecting a secondary charged particle from said wafer
charged; an energy filter disposed between said sample stage and
said detector so as to select and pass an energy of the secondary
charged particle; and a control unit for controlling said charged
particle generator on the basis of a signal from said detector.
4. A wafer inspection system using a charged particle beam,
comprising: a charged particle source; a first deflector for
scanning a wafer on which a pattern including a contact hole is
formed with a primary charged particle beam from said charged
particle source; an objective lens for irradiating said wafer on
which the pattern including the contact hole is formed with the
primary charged particle beam; a sample stage for holding said
wafer; a positive charged particle generator for positively
charging the surface of said wafer placed on said sample stage and
the side wall of said contact hole formed on said wafer; a
deflector for irradiating a predetermined area in said wafer
positively charged; a detector for detecting a secondary charged
particle from said wafer positively charged; a decelerator which is
provided for said sample stage and operates so as to decelerate the
primary charged particle beam and accelerate the secondary charged
particle; and a second deflector filter disposed between said first
deflector and said objective lens, for separating the primary
charged particle and the secondary charged particle from each
other, wherein an inspection is conducted on said contact hole on
the basis of a signal from said detector.
5. The wafer inspection system using a charged particle beam
according to claim 4, wherein said decelerator supplies a negative
voltage.
6. The wafer inspection system using a charged particle beam
according to claim 4, wherein said second deflector is an EXB type
deflector.
7. A wafer inspection system using a charged particle beam,
comprising: a sample stage for holding a sample; a first charged
particle beam source for supplying a first charged particle beam to
a sample having a hole pattern; a second charged particle beam
source for supplying a second charged particle beam; a switch for
making a switch between said first charged particle beam and said
second charged particle beam to irradiate said sample having the
hole pattern with the selected charged particle beam; an objective
lens for irradiating said sample irradiated with said first or
second charged particle beam with a third charged particle beam;
and a detector for detecting a fourth charged particle from said
sample, wherein an inspection is conducted on said hole pattern on
the basis of a signal from said detector.
8. A wafer inspection process using a charged particle beam,
comprising: a step of holding a wafer on which a pattern including
a hole pattern is formed on a sample stage; a step of charging the
surface of said wafer placed on said sample stage and the side wall
of said hole pattern formed on said wafer with a positive charged
particle; a deflecting step of scanning and irradiating said wafer
with a primary charged particle beam; a step of detecting a
secondary charged particle from said wafer positively charged by a
detector; and a step of determining whether said hole pattern is
good or not on the basis of a signal from said detector.
9. The wafer inspection process using a charged particle beam
according to claim 8, wherein as said charging step, a step of
setting a voltage of the surface of said wafer to a range from 5
volts to 50 volts is included.
10. The wafer inspection process using a charged particle beam
according to claim 8, wherein as said charging step, a step of
controlling irradiation energy of said positive charged particle to
a range from 100 electron volts to 1,000 electron volts is
included.
11. A wafer inspection system using a charged particle beam,
comprising: a charged particle source; an objective lens for
irradiating a wafer on which a pattern including a hole pattern is
formed with a primary charged particle beam from said charged
particle source; a sample stage for holding said wafer; a charged
particle generator for positively charging the surface of said
wafer placed on said sample stage and the side wall of said hole
pattern formed on said wafer; a deflector for irradiating a
predetermined area in said wafer positively charged with a primary
charged particle beam; a detector for detecting a secondary charged
particle from said wafer positively charged; and an image
processing unit for estimating a thickness of a residual film on
the bottom of said hole pattern according to a contrast of an image
of said secondary charged particle detected.
12. A wafer inspection process using a charged particle beam,
comprising: a step of holding a wafer on which a pattern including
a hole pattern is formed on a sample stage; a step of charging the
surface of said wafer placed on said sample stage and the side wall
of said hole pattern formed on said wafer with a positive charged
particle; a deflecting step of scanning and irradiating said wafer
with a primary charged particle beam; a step of detecting a
secondary charged particle from said wafer positively charged by a
detector; and a step of estimating a thickness of a residual film
on the bottom of said hole pattern according to a contrast of an
image of said secondary charged particle detected.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a wafer inspection technique using
a charged particle beam and, more particularly, to an inspection
technique using a charged particle beam such as an electron beam
for detecting a foreign matter or a defect on a wafer such as a
semiconductor wafer having a fine circuit pattern.
As a method of evaluating a semiconductor waver having a fine
circuit pattern with an electron beam, a technique of conducting a
higher-precision inspection of higher throughput adapted to the
larger diameter of a wafer and a finer circuit pattern is being
practically used. For example, as disclosed in Japanese Patent
Application Laid-Open No. H06-139985, a method of conducting an
inspection for a defect by using contrast of a secondary electron
beam generated due to surface potential variations is known.
In a method of detecting an electric defect from voltage contrast,
an electron beam is emitted before an inspection to preliminarily
positively or negatively charge the surface of a wafer, and a
secondary electron image is acquired, thereby enabling voltage
contrast to be increased. An example of a method of positively
charging the surface of a wafer is disclosed in Japanese Patent
Application Laid-Open No. 2000-208085, where a pattern such as a
contact hole in which a plug is buried is inspected by irradiating
the surface of a wafer with an electron beam to positively charge
the surface and, after that, voltage contrast is obtained.
Although the method of conducting an inspection on a circuit in
which a plug is buried is described in the above publications, a
method of conducting an inspection on the bottom of a pattern
having very a large step such as a hole after dry etching is not
described.
On the other hand, a technique of observing the bottom of a hole
pattern from an image of secondary electrons discharged when the
hole pattern is irradiated with an electron beam is known. By
conventional scanning electron microscopes, however, it takes time
to observe an object in a limited field of view at a high scaling
factor. It is therefore impossible to observe the entire surface of
a wafer and detect a defect.
An example of an inspection method of negatively charging the
surface of a wafer and detecting a contact hole with an open
contact failure is disclosed in the above-described Japanese Patent
Application Laid-open No. H06-139985 in which the surface of a
wafer is negatively charged by being irradiated with an electron
beam with low energy and, after that, a secondary electron image is
obtained. In the method, by using the fact that when a residual
film exists on the bottom of a hole, the potential of the opening
is changed by the residual film, and the diameter of the hole
becomes seemingly small, a hole with an open contact failure is
detected.
According to the method, however, an object in a limited field of
view is observed at a high scaling factor over long time, and it is
impossible to observe the entire surface of a wafer to detect a
defect. Since an electron beam is preliminarily emitted to
negatively charge the surface of a wafer and, after that, a
secondary electron image is captured and further, since irradiation
electron energy used to negatively charge the surface of a wafer
and that used to acquire a secondary electron image are largely
different from each other, it is difficult to set an electron beam
optics unit and an inspection cannot be efficiently conducted on
the entire surface of a wafer. Since the wafer has to be irradiated
with an electron beam twice or more, the whole surface of a wafer
cannot be efficiently inspected.
A conventional inspection system using an electron beam has
problems as described below.
In a conventional inspection system using an electron beam, a
defect is detected from contrast obtained due to potential
variations which occur on a wafer having a circuit pattern.
However, it is difficult to detect the state of the bottom of a
pattern having a large step, such as a contact hole with an open
contact failure, with high sensitivity by detecting a secondary
electron signal from the bottom portion of the pattern.
Particularly, most of secondary electrons from the bottom of a hole
pattern having a high aspect ratio are hindered by side walls and
cannot be detected. It is therefore difficult to detect a hole
pattern with an open contact failure.
By a conventional scanning electron microscope, although the shape
of the bottom of a hole pattern and a foreign matter can be
detected, it is difficult to detect, for example, a hole having an
open contact failure. By the conventional scanning electron
microscope, observation is made at high a scaling factor with high
spatial resolution. Consequently, scan speed is low, the scan range
is narrow, and it is impossible to scan a large area such as a
wafer required for a defect detector at high speed.
In the method of negatively charging the surface of a wafer and
detecting a contact hole with an open contact failure, the electron
beam accelerated to low speed is emitted to negatively charge the
surface of the wafer and, after that, a secondary electron image is
captured. However, in the method, due to a large difference between
the energy of the electron beam emitted to negatively charge the
surface of the wafer and that of the electron beam emitted to
obtain a secondary electron image, it is difficult to emit the
electron beams by using the same electron source. Further, the
electron beam is emitted once to negatively charge the surface of
the wafer and, after that, the secondary electron image is observed
at a high scaling factor with high spatial resolution.
Consequently, the scan speed is low, the scan range is narrow, and
it is impossible to scan a large area such as a wafer at high speed
required for the defect detector. Thus, the entire surface of a
wafer cannot be efficiently inspected.
Further, in the conventional apparatuses, the surface of a wafer is
negatively charged and the opening is evaluated. Consequently,
according to the kind and material of a semiconductor circuit
pattern, the kind of a semiconductor device which can be evaluated
is limited. There is a problem such that sensitivity of detection
of a hole with a contact hole failure varies according to the kind
of a circuit pattern.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide, as a
technique solving the problems, of conducting an inspection of a
wafer being subjected to a semiconductor manufacturing process, a
wafer inspection system and a wafer inspection process for
inspecting a pattern having a large step such as a hole pattern for
a defect at high speed and with high precision. Another object of
the invention is to provide a technique contributing optimization
of a semiconductor manufacturing process by using defect
information such as an open contact failure of a hole. Further
another object of the invention is to provide a technique
contributing to increase reliability of a semiconductor device by
detecting an abnormal process at an early stage and taking a
measure in the control of a semiconductor manufacturing
process.
First, the method of carrying out an inspection by positively
charging the surface of a wafer will be described. The principle of
the invention in which a secondary electron emitted from the bottom
of a hole is detected will be described by referring to FIGS. 2A
and 2B.
An image of a hole pattern is captured by a conventional inspection
system using an electron beam. For example, when the irradiation
energy of the electron beam is 500 eV (electron volts) and the
aspect ratio is 4 or less, secondary electrons 34 exhausted from
the bottom of a hole are easily detected. An open hole is observed
light and a hole with an open contact failure is observed dark.
However, when the aspect ratio is high, as shown in FIG. 2A, most
of the secondary electrons 34 from the bottom of the hole are
interrupted by side walls 35. Consequently, the open hole is also
observed dark, so that a hole with an open contact failure cannot
be detected.
To deal with the problem, means for preliminarily irradiating the
surface of a wafer with an electron beam or the like to charge the
surface 36 of the wafer to a desired voltage before capturing a
secondary electron image used for inspection is provided. As shown
in FIG. 2B, when the surface 36 of the wafer 36 is positively
charged, a part of the secondary electrons 34 emitted from the
bottom of the hole is accelerated upward and can be efficiently
detected. Further, the secondary electrons 34 emitted from the
bottom of the hole can be accelerated. Therefore, when the
secondary electron 34 emitted from the bottom of the hole collides
with the sidewall 35 of the hole, a secondary electron is further
emitted from the side wall 35. A part 37 of the secondary electrons
emitted from the side wall 35 is accelerated toward the opening and
can be detected by a detector. As a result, the secondary electrons
35 emitted from the bottom of a hole of high aspect ratio can be
pulled out and detected, and information such that the hole is open
or has an open contact failure can be obtained. At this time,
according to the voltage for charging the surface 36, the aspect
ratio and the hole diameter by which the hole can be detected are
determined. Therefore, means for controlling the surface 36 of a
wafer to a desired charging voltage is provided.
The voltage of charging the surface 36 of a wafer at the time of
detecting whether a hole having a high aspect ratio is open or has
an open contact failure is determined by the aspect ratio, hole
diameter, and kind and thickness of an insulating film around the
hole. For example, to detect whether a hole having an aspect ratio
of 10 formed in a silicon oxide film is open or has an open contact
failure, it is necessary to charge the surface 36 of the wafer to 5
V or higher. Therefore, means for determining a charging voltage
with reference to a prestored database is provided. In the
invention, for a hole pattern having a step, it is desirable to set
the charging voltage of a wafer in a range from 5 V to 50 V.
A method of charging the surface 36 of a wafer to a desired
positive voltage will now be described. When the surface of a wafer
is a silicon oxide film or a insulating film made of an organic
material, as an electron beam 38 for charging, an electron beam is
emitted with irradiation energy in the range from 100 eV to 1000 eV
so that secondary electron discharge efficiency becomes 1 or
higher. An electron beam optics unit for charging a wafer can be
also used as an electron beam optics unit used to capture an
inspection image. Also, means for controlling the voltage for
charging the surface 36 of the wafer by applying an optimum voltage
to an electrode 32 mounted on the top face of the wafer and
generating an electric field on the top face of the wafer is
provided.
To inspect a large area of a wafer or the like at high speed, as
the electron beam 38 for charging a wafer, an electron beam having
spatial resolution which is lowered as compared with that for
capturing an image can be used. Further, means is provided for
efficiently positively charging the surface 36 of a wafer and
conducting an inspection during movement of the wafer, which is
realized by, as a method of scanning the electron beam 38 for
charging a wafer, dividing the wafer into a plurality of inspection
areas and alternately performing charging of the wafer and
capturing of a secondary electron image.
A method of inspecting a hole by using the negative charging will
now be described. The principle of detecting a defect by using the
negative charging will be described with reference to FIGS. 3A to
3C. When the surface of a wafer is negatively charged, as shown in
FIG. 3A, open holes 40 are observed darker than an oxide film
surrounding the holes. In the case of the hole with an open contact
failure, an oxide film 41 residing on the bottom is negatively
charged. A potential distribution in an open hole shown in FIG. 3B
and that in the hole with an open contact failure shown in FIG. 3C
are different from each other. In the open hole, due to a large
difference between the negative charging voltage on the bottom of
the hole and that on the surface 36, a secondary electron emitted
from the bottom of the hole does not easily go out from the hole.
On the other hand, the bottom of the hole 41 with an open contact
failure is negatively charged, so that secondary electrons emitted
on the bottom of a hole are detected more easily than the open
hole. The closer the distance to the outer periphery of the hole
is, the higher the signal intensity of a secondary electron to be
detected is. As shown in FIG. 3A, the secondary electron image of
the hole 41 with an open contact failure is observed in such a
manner that the signal intensity of the peripheral portion of the
hole 41 is higher than that of the open hole 40 and the diameter of
the hole 41 is smaller than that of the open hole 40. In the case
where a contact hole 42 is tapered, the diameter of the contact
hole 42 is observed larger than that of the open hole 40.
At this time, by the voltage for charging the surface, the aspect
ratio at which the inspection can be conducted and the thickness of
a residual film on the bottom which can be detected are determined.
Consequently, means for controlling the surface to a desired
negative charging voltage and means for detecting the difference in
dimensions of holes in a secondary electron image are provided.
In the case of charging the surface of a wafer to a desired
negative voltage, when the surface of the wafer is a silicon oxide
film or an insulating film made of an organic material, an electron
beam having an electron beam irradiation energy of 1,000 eV or
higher with which the secondary electron emission efficiency is
lowered is emitted. Means for passing a heavy current sufficient to
negatively charge the surface of a wafer by using an electron
source for capturing an image is provided. Further, means for
applying an optimum voltage to the electrode 32 mounted on the top
face of a wafer to efficiently negatively charging the surface of
the wafer is also provided. By the electric field generated on the
top face of the wafer, the secondary electrons emitted from the
surface of the wafer can be efficiently returned to the surface of
the wafer. Thus, the surface of the wafer can be charged to a
desired negative voltage by using the electron source for capturing
an image.
As described above, by adjusting the irradiation energy of the
electron beam and the voltage of the electrode 32 mounted on the
top face of the wafer 36, the surface 36 of the wafer can be
controlled to an arbitrary positive or negative charging voltage by
the single device. As a result, irrespective of the circuit pattern
and the material of a semiconductor device, various semiconductor
circuits can be inspected at high speed.
A method of controlling the voltage for charging the wafer to a
desired positive or negative voltage will now be described. A wafer
is moved to a chip for adjusting irradiation parameters, scanned
and irradiated with an electron beam for charging, and scanned and
irradiated with an electron beam for capturing an image, and a
secondary electron image is captured. At the time of capturing a
secondary electron image, secondary electrons are detected by using
an energy filter 13. As the energy filter 13, an energy filter for
detecting secondary electrons equal to or higher a threshold or
equal to or lower than a threshold can be used.
In the case of capturing an image by using the energy filter for
detecting secondary electrons equal to or higher than a threshold,
means is provided for automatically measuring the voltage for
charging the surface of a wafer by repeating operations of fixing a
filter voltage of the energy filter 13, capturing a secondary
electron image, after that, moving the wafer to a position where
precharging is performed and a secondary electron image is
captured, fixing the threshold of the energy filter at the second
value, and capturing a secondary electron image.
As another method of measuring the charging voltage, a secondary
electron image is captured while scanning a filter voltage of the
energy filter 13 and measuring the charging voltage from the
captured secondary electron image. Means for measuring the charging
voltage by using the methods and optimizing the energy of the
electron beam for charging, the beam current, and the electrode
voltage so that the surface of a wafer is charged with a desired
charging voltage is provided. Further, means for optimizing the
irradiation parameters of an electron beam emitted to capture a
secondary electron image is provided.
After adjusting the electron beam for charging and the electron
beam for capturing a secondary electron image, an inspection is
actually conducted. In the case of capturing a secondary electron
image at the time of an inspection, a secondary electron image can
be usually captured without using the energy filter 13. However,
means for capturing a secondary electron image by using the energy
filter 13 in specific cases is provided. Means for optimizing the
set value of the energy filter from the secondary electron image
captured at the time of measuring the charging voltage is provided.
By filtering the secondary electron energy and capturing an image,
a defect can be detected with high sensitivity.
A mechanism for capturing a secondary electron image by using the
above methods, comparing the captured secondary electron image with
a secondary electron image of the same pattern captured in another
area on the wafer, and thereby detecting a defect is provided.
Further, a mechanism of calculating the contrast and size of a hole
is provided, and a mechanism of automatically determining the kind
of a defect from the contrast and size of a hole with an open
contact failure is provided. Further, means for displaying a result
of determination of a defect and a distribution of defects in the
plane of a wafer is provided.
First, a method of detecting a defect from a secondary electron
image captured by positively charging the surface of a wafer will
be described. In the case where the surface of a wafer is
positively charged, a secondary electron image of an open hole is
observed light. In the case of a hole with an open contact failure,
the oxide film residing on the bottom is charged, so that the hole
is observed darker than the open hole. In the case where the
contact hole is tapered, the hole is observed light and large.
Means for automatically detecting a hole with an open contact
failure from variations in the contrast and hole diameter and
determining the kind of the defect is provided. The thicker the
oxide film residing on the bottom is, the darker the hole with the
open contact failure is observed. Means for calculating the
thickness of the film remaining on the bottom on the basis of
brightness of the hole with an open contact failure is
provided.
On the other hand, a method of positively charging the surface of a
wafer and detecting a short circuit of a semiconductor circuit is
provided. According to the invention, the surface of a wafer is
positively charged and a hole with an open contact failure can be
detected. As a result, both a short circuit of a semiconductor
circuit and a hole with an open contact failure can be detected by
the same system.
Next, a method of detecting a failure in the case of a material of
the surface of a wafer which is not easily positively charged like
a polysilicon mask, or in the case where the material of the bottom
of the hole does not conduct a current unlike an insulating film
will be described. When the surface of such a wafer is positively
charged, a secondary electron image of an open contact failure is
observed dark. Since the electric field in the opening in the case
of a hole with an open contact failure and that in the case of an
open hole are different from each other, the hole with an open
contact failure is observed darker than the open hole.
Consequently, means for determining the hole with the open contact
failure on the basis of the size of the hole and automatically
determining the kind of the defect is provided. Means for
calculating the thickness of a film residing on the bottom from the
size of the hole with an open contact failure is provided.
Further, a method of determining a defect from a secondary electron
image captured at the time of negatively charging the surface of a
wafer will be described. In the case of negatively charging the
surface of a wafer, an open hole is observed dark in a secondary
electron image. In the case of a hole with an open contact failure,
the oxide film residing on the bottom is charged and the electric
field of the opening changes, so that the hole is observed smaller
than an open hole. When a contact hole is tapered, it is observed
larger than the open hole. Consequently, means for detecting a hole
with an open contact failure on the basis of the size of the hole
and automatically determining the kind of the defect is provided.
Means for calculating the thickness of the film residing on the
bottom from the size of the hole with the open contact failure is
provided.
As a result, whether or not there is a defect such as a hole with
an open contact failure in a hole pattern can be determined at high
speed. Further, a mechanism of finely adjusting manufacturing
parameters in a semiconductor device manufacturing process from the
detected defect information is provided. By the mechanism, the
factor of occurrence of the defect can be estimated from the kind
of the defect and a wafer in-plane distribution, and the parameters
of manufacturing a semiconductor device can be finely adjusted.
Further, a mechanism of adding a process of reducing defects in a
semiconductor device on the basis of the detected defect
information to a semiconductor manufacturing process is provided.
Consequently, the semiconductor manufacturing process can be
optimized at an early stage from the obtained defect information
such as a hole with an open contact failure. An abnormal process
can be found from the kind of the wafer and the distribution of
defects in the plane of the wafer at an early stage, the factor of
occurrence of the defect can be estimated at an early stage, and
the reliability of the semiconductor device can be increased.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a configuration diagram showing an example of a
semiconductor inspection system of the invention.
FIGS. 2A and 2B are diagrams for explaining the principle of
detecting secondary electrons generated from the bottom of a hole
used in the invention.
FIGS. 3A, 3B, and 3C are diagrams for explaining the principle of
detecting a defect by negative charging used in the invention.
FIG. 4 is a diagram showing an example of an inspection flow in the
invention.
FIG. 5 is a diagram showing charging voltage dependency of
brightness of a secondary electron image of holes.
FIG. 6 is an explanatory diagram showing an example of a beam scan
method.
FIG. 7 is a diagram showing an example of a method of setting a
filter voltage.
FIGS. 8A and 8B are diagrams showing filter voltage dependency of
signal intensity of an oxide film and signal intensity of
holes.
FIGS. 9A to 9F are diagrams for explaining an example of the beam
scan method.
FIGS. 10A and 10B are diagrams showing an example of a secondary
electron image of a contact hole pattern and a defect determining
flow, respectively.
FIG. 11 is a diagram showing residual film thickness dependency of
contrast of a hole pattern.
FIG. 12 is an explanatory diagram of the case where a pn junction
is formed.
FIG. 13 is a diagram showing an example of a defect distribution
displayed on a wafer map.
FIG. 14 is a schematic cross section showing an example of a
semiconductor device having a hole pattern inspected by the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the invention will be described hereinbelow with
reference to the drawings.
First Embodiment
In a first embodiment, an example of method and system for
inspecting a hole pattern after dry etching will be described. FIG.
1 shows the configuration of an inspection system for a
semiconductor device in the embodiment.
An inspection system 1 for a semiconductor device includes an
electron beam optics unit 2, a stage unit 3, a wafer handling unit
4, a vacuum unit 5, an optical microscope unit 6, a control unit 7,
and a control unit 8. The electron beam optics unit 2 has an
electron gun 9, a condenser lens 10, an objective lens 11, a
detector 12, an energy filter 13, a deflector 14 (for example, EXB
deflector), an electrode 32 on the top face of a wafer, and a
height measure sensor 15. The stage unit 3 includes an XY stage 16,
a wafer holder (sample stage) 17, and a retarding power supply 19
for applying a negative voltage to the holder 17 and wafer 18. To
the XY stage 16, a position detector by laser length measurement is
attached. The wafer handling unit 4 carries the wafer 18 among a
wafer case 20, a wafer loading unit 22, and the XY stage 16. The
control unit 7 includes a signal detection control unit 22, a
blanking control unit 23, a beam deflector control unit 24, an
electron beam optics control unit 25, a height measurement unit 26,
a stage control unit 27, and an electrode control unit 33. The
control unit 8 is constructed by a graphical user interface and
user interface unit 28, an image processing unit 29, a data storage
unit 30, and an outer server 31.
A defect detecting method will be described in accordance with an
inspection flow. FIG. 4 shows the inspection flow. First, location
number in the case of a wafer to be inspected is designated on the
graphical user interface 28 (step 43). As information of the wafer
to be inspected, information such as aspect ratio, hole diameter,
and material of a pattern is input. Further, as irradiation
parameters of an electron beam 38 for charging the wafer,
parameters such as electron beam irradiation energy, beam current,
and beam diameter are input, and a voltage for charging the surface
of the wafer is designated. Further, as inspection parameters, an
inspection area, electron beam irradiation energy at the time of
capturing a secondary electron image, beam current, scan speed, and
scan size are input (step 44). From the information of a wafer to
be inspected, inspection parameters in a database can be also used.
The information of the wafer to be inspected, electron beam
irradiation parameters, and inspection parameters can be also input
from the outer server 31.
As an electron beam irradiation parameter at the time of positively
charging the surface of a wafer, for example, the irradiation
energy can be set to a value in a range from 100 eV to 1000 eV so
that the electron beam emission efficiency becomes 1 or higher. It
is desirable to set the irradiation energy at the time of
inspection to the same value as the electron beam for charging a
wafer. By setting the irradiation energy at the time of inspection
and that of the electron beam for charging the wafer to the same
level, the electron beam for charging the wafer and the electron
beam for detecting a secondary electron image can be emitted from a
single electron source. By emitting an electron beam of relatively
low energy, not only the surface of the wafer is positively charged
but also an inspection can be conducted while reducing a damage on
the semiconductor device.
A set value of a voltage for charging the wafer is determined
mainly from the aspect ratio of the hole pattern. FIG. 5 shows
charging voltage dependency of brightness of a secondary electron
image of the holes. Secondary electrons from the bottom of a hole
having the aspect ratio of up to 4 can be obtained even when the
charging voltage is 5 V or less. When the aspect ratio becomes 8 or
higher, as shown in FIG. 5, the wafer has to be charged to 10 V or
higher. From a database of dependency on the aspect ratio of a
necessary charging voltage preliminarily obtained, the set value of
the charging voltage can be also determined. After completion of
setting of the inspection parameters, an inspection is started. The
inspection parameters can be also preset by using an off-line
computer.
When the inspection is started, the wafer 18 is carried to the
inspection system. The wafer 18 is carried from the case into the
wafer loading unit. After that, the wafer loading unit is evacuated
and the wafer 18 is loaded into an inspection chamber which is
already evacuated (step 45).
After completion of loading of the wafer, on the basis of the input
inspection parameters, the electron beam irradiation parameters at
the time of capturing a secondary electron image are set in the
units by the electron beam optics control unit 25. The stage 16 is
moved so that a beam alignment pattern on the wafer holder 17 is
positioned below the electron beam optics unit 2 (step 46). After
that, an electron beam image is captured, setting of focus,
astigmatism, and the detectors is adjusted to thereby control the
contrast and the like of an image (step 47). Simultaneously, the
height of the wafer 18 is measured by the height measure sensor 15,
and the correlation of the height information and the focus
condition of the electron beam is calculated by the wafer height
measurement unit 26. After that, when an electron beam image is
captured, without performing focusing each time, the parameters can
be automatically adjusted to the focus parameters from a result of
the wafer height measurement.
When the image adjustment at the time of capturing a secondary
electron image is completed, the irradiation parameters of the
electron beam 38 for charging the wafer are adjusted (step 48).
First, the stage 16 is moved so that the pattern for adjusting the
charging voltage is set below the electron beam optics unit 2. As
the electron beam 38, a beam having the diameter larger than that
of a beam for capturing a secondary electron image by about 100 to
1000 times can be used.
FIG. 6 shows an example of a method of scanning the electron beam
38 for charging the wafer and the beam for capturing a secondary
electron image. After irradiating a first scanning area 57 with the
electron beam for charging, while scanning the electron beam for
capturing a secondary electron image, a secondary electron image in
a second scanning area 58 included in the first scanning area 57 is
captured. The first scanning area 57 is a sufficiently large area
including the second scanning area 58. At this time, a secondary
electron image is captured by using the energy filter 13.
As an example, an energy filter of a type that captures secondary
electrons equal to or larger than a threshold is used. By the
energy filter, electrons having energy equal to or higher than a
voltage applied to the filter are detected. First, the threshold is
set to V0 and a secondary electron image in the secondary scanning
area 58 is captured. Signal intensities in holes in the secondary
electron image and a portion of an oxide film are stored in the
data storage unit 30. Subsequently, a secondary electron image in a
third scanning area 59 which is included in the first scanning area
57 but does not include the second scanning area 58 is captured. At
this time, the energy filter 13 is set to a threshold V1. Signal
intensities in holes and the portion of the oxide film of the
secondary electron image are stored into the data storage unit 30.
Until the filter voltage at which the signal intensity in the
portion of the oxide film changes is obtained, the process of
capturing a secondary electron image in an nth scanning area 60
included in the first area 58 by using a filter voltage Vn is
repeated.
A method of setting the filter voltage Vn at this time will be
described by referring to FIG. 7. A signal 61 from the SiO2 surface
charged to a voltage changes according to the filter voltage as
shown in FIG. 7. At V0, a secondary electron of all the energy is
captured, so that the signal intensity is the maximum value I0. At
V1, most secondary electrons are not detected, so that the signal
intensity is the minimum value I1. The values V0 and V1 are set,
for example, in a range from 50 V to -20 V. Further, the values
from V2 to Vi are set between V0 and V1, for example, at intervals
of 10 V. When the signal intensity becomes equal to or higher than
(I0+I1)/2 and equal to or lower than I0, for example, two more
voltages are set at an interval of 5 V. When the signal intensity
becomes equal to or higher than I1 and equal to or lower than
(I0+I1)/2, Vn+5V is set as Vn+1. From the signal intensities, Vm at
which the signal intensity is (I0+I1)/2 can be obtained. The
voltage for charging the wafer is calculated from a shift amount of
a curve of filter voltage dependency of a signal intensity 62 from
the Si substrate preliminarily calculated.
While measuring the charging voltage in such a manner, the electron
beam for charging the wafer is adjusted until a desired charging
voltage is obtained (step 49). Means for measuring the charging
voltage by using such a method and optimizing the current value of
the electron beam 38 for charging the wafer, electrode 32, and beam
energy so that the surface of the wafer is charged to a desired
charging voltage is provided.
An actual inspection can be also conducted by using the energy
filter 13. The set value of the filter voltage in an inspection can
be also determined at the time of measuring the charging voltage. A
method of determining the set value of the filter voltage will now
be described. A signal intensity I.sub.SiO2 from the SiO.sub.2 film
and a signal intensity I.sub.Hole from a hole are calculated from a
secondary electron image captured at the time of measuring the
charging voltage.
FIG. 8 shows dependency of the filter voltage of intensity 64 from
the SiO2 area surrounding the holes and the signal intensity 63
from the holes. Further, contrast C=(I.sub.Hole
-I.sub.SiO2)/I.sub.SiO2 is calculated, and a filter voltage
V.sub.MAX by which the contrast becomes the maximum is determined
as the set value used at the time of the inspection. The determined
set value is stored in the data storage unit 30.
After that, when the setting of the electron beam irradiation
parameters and image adjustment are completed, alignment is
performed by using two points on the wafer 18 (step 50). The wafer
18 to be inspected is disposed in predetermined first coordinates,
and an optical microscope image of a circuit pattern formed on the
wafer 18 to be inspected is displayed on a monitor in the graphical
user interface 28 and compared with an optical microscope image of
an equivalent circuit pattern in the same position prestored for
position turn calibration, thereby calculating a position
calibration value in the first coordinates (step 51).
In the first coordinates, the optical microscope image is switched
to an electron beam image. The optical microscope unit 6 and the
electron beam optics unit 2 are disposed in positions apart from
each other by a predetermined distance and the distance is stored
as a known parameter in the system. Consequently, the optical
microscope image and the electron beam image can be arbitrarily
switched to each other. With respect to the electron beam image as
well, an image of a circuit pattern is prestored for position turn
calibration in a manner similar to the optical microscope image. By
comparing the stored electron beam image with a captured electron
beam image, the position calibration value of the first coordinates
more accurate than that of the optical microscope is
calculated.
Next, the position is moved from the first coordinates to second
coordinates which are apart from the first coordinates by a
predetermined distance, where a circuit pattern equivalent to that
in the first coordinates exists. Similarly, an optical microscope
image is captured and compared with a circuit pattern image stored
for position turn calibration, and a position calibration value and
a turn deviation amount from the first coordinates are calculated
from the second coordinates. Further, also in the second
coordinates, the optical microscope image is switched to the
electron beam image and compared with the electron beam image of
the prestored circuit pattern, and an accurate position calibration
value in the second coordinates is calculated. On the basis of the
calculated turn deviation amount and positional deviation amount,
in the control unit 25 and the beam deflector control unit 24, the
scan deflection position of the electron beam is calibrated so as
to correspond to the coordinates of the circuit pattern.
When alignment of the wafer 18 to be inspected is completed in such
a manner, the wafer 18 to be inspected is irradiated with an
electron beam 38 for charging the wafer, an electron beam image is
obtained, and brightness is tuned (step 52). At the time of
capturing an electron beam image on the basis of the inspection
parameter file, since an electron beam current, electron beam
irradiation energy, a voltage to be applied to the energy filter
13, the detector 12 to be used, and the gain of a detection system
are set, an electron beam image is captured by setting those
parameters.
After completion of the brightness adjustment, an inspection is
carried out (step 53). An inspection area is preliminarily
designated in an inspection parameter file. In the case of emitting
the electron beam 38 for charging the wafer, the wafer is divided
into a plurality of inspection areas. By alternately repeating the
charging of the wafer and capturing of a secondary electron image,
the surface of the wafer can be efficiently positively charged
during the time of movement of the wafer.
FIG. 9 shows an example of the electron beam scanning method.
First, a first irradiation area 66 is irradiated and scanned with
the electron beam 38 for charging the wafer as shown in FIG. 9A
with the set parameters. A first scanning area 67 is scanned with
the electron beam 39 for detecting the secondary electrons as shown
in FIG. 9B and a secondary electron image is obtained.
Subsequently, as shown in FIG. 9C, a second irradiation area 68 is
irradiated with the electron beam 38 for charging the wafer, and a
second scanning area 69 is scanned with the electron beam 39 for
detecting the secondary electrons. At this time, the electron beam
38 for charging the wafer can be emitted while moving the wafer. In
such a manner, the electron beam 38 for charging the wafer can be
emitted during the period of movement of the wafer, so that the
inspection can be conducted without spending extra time for
charging the wafer.
By repeating the operations as shown in FIG. 9, the whole surface
of the wafer can be inspected. At the time of the inspection, while
continuously moving the XY stage 16, a predetermined area in the
wafer 18 to be inspected is irradiated with an electron beam. While
sequentially forming electron beam images, an image signal is
compared with a signal stored in the data storage unit 30, and the
images are sequentially stored in the data storage unit 30. In such
an inspection, the detector 12 is preset by an inspection parameter
file 204. A voltage can be also applied to the energy filter 13
disposed at the ante-stage of the detector 12.
A method of determining a defect of a hole will now be described.
For example, in the case where the film is made of silicon oxide
(SiO.sub.2), after a secondary electron image is captured, a defect
is determined by the following method.
FIG. 10A shows an example of a secondary electron image of a
pattern in which contact holes are formed and FIG. 10B is a defect
determining flow. A hole 72 with an open contact failure shown in
FIG. 1A is observed darker than an open hole 70. On the other hand,
a hole 72 with an irregular tapered angle is observed lighter and
bigger than the open hole 70.
FIG. 11 shows residual film thickness dependency of contract of
holes. The thickness of a residual film of zero indicates contrast
of an open hole. Since the hole 71 with an open contact failure is
observed darker than the open hole 70, the hole 71 with an open
contact failure can be determined as a defect. At this time, the
contrast of the hole 71 with the open contact failure decreases as
the thickness of the residual film increases, so that the thickness
of the residual film of the hole 71 with the open contact failure
can be also estimated from the contrast of the hole.
The defect determination is made from the captured secondary
electron image as follows. First, as shown in FIG. 10B, the shapes
of secondary electron images are compared with each other (step
73). When the shape of the obtained image does not coincide with
that of the reference secondary electron image, an irregular shape
is determined. Further, the captured image is compared with a
secondary electron image for comparing the contrast of holes (step
74). When the captured image has the contrast which is almost the
same as that of the reference image, the hole in the captured image
is determined as an open hole. When the hole in the captured image
is darker than that in the reference image, an open contact failure
or contamination in the hole is determined. When the contrast of
the hole in the captured image is brighter than that in the
reference image, the hole in the captured image is determined as a
hole with an irregular tapered angle. Consequently, the hole 71 is
determined as a hole with an open contact failure, and the hole 72
is determined as a hole with irregular tapered angle.
Further, the thickness of the residual film can be also estimated
from the contrast data of the hole with open contact failure
prestored in the data storage unit 30 or the outer server 31 (step
75). Data can be retrieved from a database of changes in contrast
according to the thickness of the residual film in accordance with
parameters such as the aspect ratio of the hole, hole diameter,
charging voltage, and material of an insulating film.
There is a case such that a junction of a different kind is
included in the bottom of a contact hole. Since the resistance of
the bottom of the open hole varies according to the kind of a
junction, the brightness of the hole changes according to the kind
of the junction. In such a case, patterns of the same kind are
compared with each other by using information of pattern
arrangement on the wafer, thereby comparing the holes having
junctions of the same kind with each other. Particularly, when a pn
junction having an n diffusion layer as an upper layer is provided
is formed on the bottom of the contact hole, the contrast of the
hole decreases.
FIG. 12 is a diagram showing a model in the case where a pn
junction is formed. Shown in the diagram are an insulator 76
between layers, an n-type diffusion layer 77, a p-well 78, a
silicon substrate 79, and a primary electron beam 80.
On the bottom of a hole having no pn junction, when an electron
beam is emitted with a parameter that the electron beam emission
efficiency is 1 or higher, electrons are supplied from the wafer,
so that the voltage at the bottom of the hole becomes 0 V. However,
when the n-diffusion layer 77 is irradiated with an electron beam,
electrons are not supplied from the substrate 79 side because of
the pn junction, and the bottom of the hole is charged.
Consequently, the contrast becomes low. In such a case, by
optimizing the electron beam energy, the contrast can be
improved.
For example, a case where the depth of a junction is L and a
depletion layer area having a width W is formed in the junction are
a will be described. After atomic weight (A), atomic number (Z),
and density (.rho.) of the sample are determined, depth R of
intrusion of an electron is determined by the energy of the
electron. For example, when Si is irradiated with an electron beam
having incident energy of 500 eV, the depth R of intrusion of the
electron beam is 10 to 20 nm. The higher the energy of the electron
beam is, the deeper the depth R of intrusion of the electron
becomes. When the depth R of intrusion of the electron beam is
small and the electron does not enter the depletion layer area, if
the n-type diffusion layer 77 is irradiated with the electron beam
80, the surface is positively charged. When the irradiation energy
of the electron beam and the voltage charged on the surface are
adjusted to make the electron beam start entering the depletion
layer, an electron-hole pair is generated in the depletion layer,
so that resistance in the junction decreases. As a result,
electrons are supplied from the substrate 79, so that charging of
the bottom of the hole is suppressed, and the contrast of the
secondary electron of the hole can be improved.
There is a case such that a conductive material such as poly Si of
a mask is used on the surface of the wafer to be inspected. At this
time, it is difficult to charge the surface of the wafer to 5 V or
higher. On the other hand, there is a case such that the bottom of
the hole is an insulating film made of SiN or resistance of the
junction is high and a current is not easily supplied to the bottom
of the contact hole. Since the bottom of the hole is charged by
being irradiated with the electron beam, it is difficult to pull
out and detect secondary electrons emitted from the bottom of the
hole.
The method of inspecting the hole with an open contact failure in
such cases will now be described. When the surface of the wafer is
irradiated with an electron beam, even if the surface of the wafer
is charged positively, as shown in FIG. 3, the secondary electron
image of an open hole 40 is observed dark. In the case of the hole
with the open contact failure, a residual film 41 on the bottom is
charged more than the bottom of the open hole 40. By a change in
the electric field of the open hole, the hole with the open contact
failure is observed smaller than the open hole. The dimension of
the hole with failure is observed smaller as the residual film on
the bottom becomes thicker (41 in FIG. 3). When the contact hole is
tapered, the hole is observed larger than the open hole (42 in FIG.
3). Means for determining a hole with the open contact failure on
the basis of the size of the observed secondary electron image and
automatically determining the kind of the failure is provided.
Means for calculating the thickness of the film residing on the
bottom from the dimension of the hole with open contact failure on
the basis of the relation between the prestored hole dimension and
the hole with open contact failure is provided.
Coordinates, signal value, kind of the failure, size of the failure
hole, and the like of the position determined as a failure by using
a method as described above are automatically recorded and, as
shown in FIG. 13, marks each indicative of a failure are displayed
by kind in the position corresponding to the wafer map on the
graphical user interface 28. After completion of the inspection on
the area designated by the inspection parameter file, an image of
the hole with failure can be captured again (step 54 in FIG.
4).
As described above, by positively charging the surface of the
wafer, it becomes possible to conduct an inspection for the hole
with the open contact failure. On the other hand, a method of
detecting a short-circuit failure of a semiconductor circuit at
high speed by using positive charging is proposed. It enables the
hole with the open contact failure and the short circuit failure to
be inspected at high speed with high sensitivity by using the same
inspection system. Further, as will be described in the second
embodiment, the electron beam irradiation energy and the voltage of
an electrode provided on the surface of the wafer are adjusted so
as to attain a desired negative charging voltage, thereby enabling
the surface of a wafer to be controlled to a desired positive or
negative charging voltage by the same system. Thus, irrespective of
the kind and material of the circuit pattern of the semiconductor
device, defects of a plurality of kinds of a semiconductor circuit
can be detected.
FIG. 14 is a schematic block diagram of a DRAM as an example of a
semiconductor device having a hole pattern inspected by the
invention. An active region formed on a semiconductor substrate 84
is dived by a field oxide layer 83. A gate electrode 85 is formed
over the active region and covered with a spacer 86. A first
insulation layer 87 such as an oxide film is formed on the surface
and, after that, a first contact hole 88 is formed by dry etching.
The contact hole 88 is formed as a direct contact for a bit line.
After forming a bit line, a second insulation layer 89 is formed,
and a second contact hole 90 is opened. As an example of the
inspection according to the invention, the direct contact hole 88
being subjected to a DRAM manufacturing process shown in FIG. 14
and a hole 89 formed on the wiring are inspected. Further, holes
formed on the other wiring can be also inspected. Alternately, an
inspection can be also conducted after a process of developing a
mask pattern for forming a hole pattern. Shown in FIG. 14 are a
p-type diffusion layer 91, an n-type diffusion layer 92, an n-well
93, a p-well 94, and a substrate 95.
As described above, the wafer including the contact hole pattern
can be inspected and a defect can be automatically determined.
Further, a mechanism for automatically specifying a defect causing
process and a factor from a preliminarily formed database with
respect to some factors of the occurrence of defects on the basis
of the kind of a defect and a distribution of defects in the plane
of the wafer is provided. Further, a mechanism for finely adjusting
parameters of a defect causing process is provided. A mechanism for
reducing a defect on a wafer to be inspected by performing an
additional process on the wafer on the basis of detected defect
information is also provided.
An example of the mechanism for finely adjusting the parameters of
the semiconductor manufacturing process on the basis of the
inspection result will be described. In the case where a number of
holes with open contact failure occur in a concentrical shape or on
the whole surface of the wafer, time of dry etching for opening the
holes can be finely adjusted according to the thickness of a
residual film on a hole with open contact failure. In the case
where a defect such as a hole with open contact failure or a
tapered hole occurs in a specific pattern, lithography parameters
are finely adjusted or a reticle is replaced. In the case where a
number of defects occur due to condensed or rare patterns around a
semiconductor memory mat or the like, flow rate of dry etching gas
is finely adjusted, an etcher is cleaned, or the like. When a
number of foreign matters occur, a semiconductor manufacturing
device is cleaned or dry etching parameters are finely
adjusted.
On the other hand, a mechanism for adding a process capable of
reducing defects in a wafer to be tested is provided. In the case
where a number of holes with open contact failure occur due to
insufficient dry etching, dry etching can be added. When a number
of foreign matters occur, cleaning can be added. As a result, it
becomes possible to specify a process in which a failure occurs and
the cause of the failure at an early stage, and perform feedback to
a semiconductor manufacturing process such as a dry etching process
at an early stage.
Second Embodiment
In a second embodiment, a method of carrying out an inspection on a
hole pattern after dry etching and, as an example of an apparatus,
a method of negatively charging the surface of an oxide film and
conducting an inspection will be described. In the embodiment, the
semiconductor inspection system shown in FIG. 1 can be used.
In the case of charging the surface 36 of a wafer to a desired
negative voltage, when the surface 36 of the wafer is a silicon
oxide film or an insulating film made of an organic material, as an
electron beam irradiation energy for charging the wafer, an
electron beam of 1000 eV or higher at which the secondary electron
emission efficiency becomes 1 or less is emitted. The irradiation
energy of the electron beam 39 for detecting secondary electrons is
desirably set to the same value as that of the electron beam for
charging the wafer. By setting the irradiation energy at the time
of inspection and that of the electron beam for charging the wafer
to the same level, an electron beam for charging the wafer and an
electron beam for capturing a secondary electron image can be
emitted by using a single electron source. Further, to efficiently
negatively charge the surface of the wafer, an optimum voltage is
applied to the electrode 32 mounted on the top face of the
wafer.
A method of setting electron beam irradiation parameters such as
the beam energy, beam current, and electron beam irradiation time
and setting of an electrode voltage will be described. These set
values may be read from an inspection parameter data file
prestored. First, a set value of the voltage for charging the wafer
is determined mainly from an aspect ratio of a hole pattern.
A method of setting electron beam irradiation parameters so as to
satisfy a desired negative charge voltage after completion of
loading of the wafer (step 45) in the inspection flow shown in FIG.
4 will be described. As an example, a method of capturing a
secondary electron image by using an energy filter of a type that
captures secondary electrons equal to or higher than a threshold
and measuring a charging voltage is used. First, the stage 16 is
moved so that a pattern for adjusting a charging voltage is
positioned below the electron beam optics unit 2. The threshold is
set to V0 and a secondary electron image in a first area is
captured. Signal intensities of holes in the secondary electron
image and the portion of an oxide film are stored in the data
storage unit 30.
Subsequently, an energy filter sets the threshold to V1 and
captures a secondary electron image in a second area. Signal
intensities in holes in the secondary electron image in the second
area and the oxide film portion are stored in the data storage unit
30. Until a filter voltage at which the signal intensity 61 of the
oxide film portion changes is obtained, the process of capturing
the secondary electron image in an n-th area included in the first
area by a filter voltage Vn is repeated. As a method of setting the
filter voltage Vn at this time, as an example, the method described
in the first embodiment can be used. From the signal intensities,
Vm at which (I0+I1)/2 is obtained can be calculated.
The voltage for charging the wafer is calculated from a shift
amount from a curve of filter voltage dependency of signal
intensity from the Si substrate preliminarily obtained. While
changing the electron beam irradiation parameters, the charging
voltage is repeatedly measured. Until a desired charging voltage is
obtained, an electron beam is adjusted. Means for measuring the
charging voltage by using such a method and optimizing current
values of the electron beam for charging the wafer and the electron
beam for capturing an image, irradiation time, beam energy, and
electrode voltage so that the surface of the wafer is charged to a
desired charging voltage is provided.
After completion of adjusting the electron beam irradiation
parameters and images, alignment of the wafer (step 50),
calibration (step 51), and tuning of brightness (step 52) are
performed. After that, an inspection is conducted (step 53). At the
time of capturing a secondary electron image used for inspection, a
voltage is applied to the energy filter 13 disposed at the
ante-stage of the detector 12, thereby enabling detection
sensitivity to be improved.
A method of determining failure of a hole will now be described. In
the case of negatively charging the surface of a wafer, as shown in
FIG. 3, a secondary electron image of the open hole 40 is observed
dark. In the case of the hole 41 with open contact failure, the
oxide film remaining on the bottom portion is charged and the
electric field of the opening changes, so that the hole 41 is
observed smaller than the open hole. A defective hole such as the
hole 41 is observed smaller as the thickness of the film remaining
on the bottom increases. In the case of a tapered contact hole 42,
the contact hole 42 is observed larger than the open hole.
Consequently, means for determining a defective hole on the basis
of the sizes of holes in the observed secondary electron image, and
automatically determining the kind of a defect is provided. Means
for calculating the thickness of the film remaining on the bottom
from the size of the defect hole on the basis of the relation
between prestored hole size and the defective hole is provided.
There is a case such that junctions of different kinds are included
in the bottom of a contact hole. Since the resistance of the bottom
of the open hole varies according to the kind of a junction, the
size of the hole changes according to the kind of the junction. In
such a case, patterns of the same kind are compared with each other
by using information of pattern arrangement on the wafer, thereby
comparing the holes having junctions of the same kind with each
other.
With respect to the position determined as a failure by the
inspection, the coordinates, signal value, the kind of the failure,
the size of the failure, and the like in the position are
automatically recorded. FIG. 13 shows a result of the inspection.
In the inspection, a distribution 82 of holes with open contact
failure and a distribution 83 of holes with irregular shapes are
detected on the wafer 18. Marks indicative of failures are
displayed in corresponding positions on the wafer map in the
graphical user interface 28 kind by kind on the basis of the result
of classification. After completion of the inspection on the area
designated by the inspection parameter file, an image of the
failure position can be captured again (step 54 in FIG. 4).
As described above, the inspection can be conducted on the wafer
including the contact hole pattern by negatively charging the
surface of the wafer, and a failure can be automatically
determined. As a result, an inspection on a wafer to be inspected
made of a material or having a circuit pattern which is difficult
to be positively charged as shown in the first embodiment can be
also conducted.
By using the methods of the embodiments, therefore, an inspection
can be conducted on various kinds of patterns to see the presence
or absence of a failure, for example, whether, a hole is an open
hole or a hole with open contact failure in a hole pattern after
the dry etching process in a non-destructive manner. As a result
that deep holes can be evaluated non-destructively, a semiconductor
device can be manufactured in such a manner that a wafer is taken
out during a manufacturing process, subjected to an inspection and,
after the inspection, returned to the process. Since an inspection
on holes can be carried out before a wiring process, a dry etching
process development period can be largely shortened. Further, the
kind of a defect, a distribution of defects in the plane of the
wafer, and the position of the failure can be obtained at high
speed, an abnormal process can be found at an early stage, and the
factor of occurrence of the failure can be estimated in a short
period.
Although the case of the inspections using the electron beam has
been described in the foregoing embodiments, the invention can be
also applied to an inspection using a charged particle beam other
than the electron beam, for example, an ion beam.
The invention will be summarized as follows. As a first invention,
there is provided a wafer inspection system using a charged
particle beam, including: a charged particle source; an objective
lens for irradiating a wafer on which a pattern including a hole
pattern is formed with a primary charged particle beam from the
charged particle source; a sample stage for holding the wafer; a
charged particle generator for positively charging the surface of
the wafer placed on the sample stage; a deflector for irradiating a
predetermined area in the wafer positively charged with a primary
charged particle beam; and a detector for detecting a secondary
charged particle from the wafer positively charged, wherein an
inspection is conducted on the hole pattern on the basis of a
signal from the detector. In associated with the above, an electron
source is provided as the charged particle generator.
As a second invention, there is also provided a wafer inspection
system using a charged particle beam, including: a charged particle
source; an objective lens for irradiating a wafer on which a
pattern including a hole pattern is formed with a primary charged
particle beam from the charged particle source; a sample stage for
holding the wafer; a charged particle generator for positively
charging the surface of the wafer placed on the sample stage; a
deflector for scanning and irradiating a predetermined area in the
wafer charged by the charged particle generator with a primary
charged particle beam; a detector for detecting a secondary charged
particle from the wafer charged; an energy filter disposed between
the sample stage and the detector so as to select and pass an
energy of the secondary charged particle; and a control unit for
controlling the charged particle generator on the basis of a signal
from the detector.
As a third invention, there is provided a wafer inspection system
using a charged particle beam, including: a charged particle
source; a first deflector for scanning a wafer on which a pattern
including a contact hole is formed with a primary charged particle
beam from the charged particle source; an objective lens for
irradiating the wafer on which the pattern including the contact
hole is formed with the primary charged particle beam; a sample
stage for holding the wafer; a positive charged particle generator
for positively charging the surface of the wafer placed on the
sample stage; a deflector for irradiating a predetermined area in
the wafer positively charged; a detector for detecting a secondary
charged particle from the wafer positively charged; a decelerator
which is provided for the sample stage and operates so as to
decelerate the primary charged particle beam and accelerate the
secondary charged particle; and a second deflector filter disposed
between the first deflector and the objective lens, for separating
the primary charged particle and the secondary charged particle
from each other, wherein an inspection is conducted on the contact
hole on the basis of a signal from the detector. In associated with
the above, the decelerator supplies a negative voltage. The second
deflector is an EXB type deflector.
As a fourth invention, there is provided a wafer inspection system
using a charged particle beam, including: a sample stage for
holding a sample; a first charged particle beam source for
supplying a first charged particle beam to a sample having a hole
pattern; a second charged particle beam source for supplying a
second charged particle beam; a switch for making a switch between
the first charged particle beam and the second charged particle
beam to irradiate the sample having the hole pattern with the
selected charged particle beam; an objective lens for irradiating
the sample irradiated with the first or second charged particle
beam with a third charged particle beam; and a detector for
detecting a fourth charged particle from the sample, wherein an
inspection is conducted on the hole pattern on the basis of a
signal from the detector.
As an invention of a first inspection process, there is provided a
wafer inspection process using a charged particle beam, comprising:
a step of holding a wafer on which a pattern including a hole
pattern is formed on a sample stage; a step of charging the surface
of the wafer placed on the sample stage with a positive charged
particle; a deflecting step of scanning and irradiating the wafer
with a primary charged particle beam; a step of detecting a
secondary charged particle from the wafer positively charged by a
detector; and a step of determining whether the hole pattern is
good or not on the basis of a signal from the detector. In the
invention, as the charging step, a step of setting a voltage of the
surface of the wafer to a range from 5 volts to 50 volts may be
included. As the charging step, a step of controlling irradiation
energy of the positive charged particle to a range from 100
electron volts to 1,000 electron volts may be included.
As an invention of a second inspection process, there is provided a
wafer inspection process using a charged particle beam, comprising:
a step of holding a wafer on which a pattern including a hole
pattern is formed on a sample stage; a step of charging the surface
of the wafer placed on the sample stage with a negative charged
particle of energy equal to or higher than 1 kilo electron volt; a
deflecting step of scanning and irradiating the wafer with a
primary charged particle beam; a step of detecting a secondary
charged particle from the wafer negatively charged by a detector;
and a step of determining whether the hole pattern is good or not
on the basis of a signal from the detector.
As an invention of a third inspection process, there is provided a
wafer inspection process using a charged particle beam, comprising:
a step of holding a wafer on which a pattern including a hole
pattern is formed on a sample stage; a step of charging the wafer
with a first charge particle beam from a charged particle source; a
charging the surface of the wafer placed on the sample stage with a
first charged particle beam from the charged particle source; a
step of scanning and irradiating a predetermined area in the
charged wafer with a primary charged particle beam; a step of
detecting a secondary charged particle from the wafer charged by a
detector; and a step of determining whether the hole pattern is
good or not on the basis of a signal from the detector.
As an invention of a fourth inspection process, there is provided a
wafer inspection process using a charged particle beam, comprising:
a step of continuously moving a sample stage in a first direction,
irradiating a predetermined area in a wafer with a primary charged
particle beam, and determining whether a hole pattern is good or
not on the basis of a signal from a detector by using: a charged
particle source; an objective lens for irradiating a wafer on which
a pattern including a hole pattern is formed with a primary charged
particle beam from the charged particle source; a sample stage
which holds the wafer and reciprocates; a positive charged particle
generator for positively charging the surface of the wafer placed
on the sample stage; a deflector for irradiating a predetermined
area in the wafer positively charged with a primary charged
particle beam; and a detector for detecting a secondary charged
particle from the wafer positively charged; and a step of charging
the wafer with the positive charged particle beam from the positive
charged particle generator when the sample stage is continuously
moved in a second direction which is different from the first
direction.
As an invention of a fifth inspection process, there is provided a
wafer inspection process using a charged particle beam, comprising:
a step of charging a predetermined area in a pattern including a
contact hole formed on a wafer with a positive charged particle
beam; a first deflecting step of scanning and deflecting the wafer
charged by the primary charged particle beam from a charged
particle source by a first deflector; a step of detecting a
secondary charged particle from the wafer positively charged by a
detector; a decelerating step of decelerating the primary charged
particle beam and accelerating the secondary charged particle; a
step of separating the first charged particle beam and the second
charged particle from each other by a second deflector; and a step
of determining whether the contact hole is good or not on the basis
of a signal from the detector.
Further, as an invention of a sixth inspection process, there is
provided a wafer inspection process using a charged particle beam,
comprising: a step of holding a sample having a hole pattern on a
sample stage; a first charging step of supplying a first charged
particle beam to the sample; a second charging step of supplying a
second charged particle beam; a step of making a switch between the
first charged particle beam and the second charged particle beam in
accordance with a sample; a step of irradiating the sample
irradiated with the first or second charged particle beam with a
third charged particle beam; a step of detecting secondary
particles from the sample by a detector; and a step of determining
whether the hole pattern is good or not on the basis of a signal
from the detector.
As described above, according to the invention, the wafer
inspection system and the wafer inspection process capable of
conducting an inspection for a defect on a wafer such as a
semiconductor wafer having a pattern including a large step such as
a hole pattern at high speed and with high precision can be
realized. Particularly, the process development period and yield
improvement period in the semiconductor device manufacturing
process can be largely shortened, so that the improved reliability
and productivity of the semiconductor device can be achieved.
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